Disk burnishing/wiping machines are often used to burnish/wipe both sides of a disk surface (such as a fabricated disk substrate for a magnetic recording system of a hard disk drive) to ensure particles and other debris are removed and thereby make the disk surface cleaner. In this process, a disk is clamped to a spindle which rotates the disk during the burnishing process. While the disk is being rotated, two sides of a contact roller (pad) of the burnishing unit with a very fine abrasive tape move toward the disk surface simultaneously, and bring the tape surface against the disk surface with a certain pressure/force to burnish both sides of the disk surface. The particles on the disk surface are thereby removed and/or reduced. In a subsequent processing step that operates in a similar way, a wiping unit with a woven cotton tape can be applied to remove the debris on the burnished disk surface, making the disk surface smoother and cleaner consequently.
During the burnishing/wiping process, a significant parameter for process quality is the loading force which is exerted on the disk surface by the burnishing/wiping unit through the contact roller or pad. For high product yield and positive testing results, it is best that the applied loading force is very accurate and consistent. More specifically, it is best that side-to-side loading force variations and machine-to-machine loading force variations are minimal or non-existent. To achieve this, the load cell, which measures the loading force, needs to be calibrated accurately and repeatedly.
In commonly used burnishing/wiping machines, a small load cell is tightly glued in a load cell bracket which is attached in a vertical orientation to a load force adjustment mechanism. The control and feedback wiring of the load cell are routed through various machine components, and are thus hidden inside. As such, it can be difficult to calibrate the load cell for a number of reasons. First, space limitations in the burnishing machine often do not allow existing load cell calibration tools to be used. Second, the load cell is small and often positioned vertically in the burnishing machine, which can make calibration extremely difficult or virtually impossible without dismantling it. At the same time, the load cell is tightly glued to the load cell bracket, and thus dismantling it will most likely damage the load cell. Third, the load cell control/feedback wiring is hidden inside the machine and it is troublesome to disconnect this wiring. Fourth, a small protrusion on load cell surface, which effectively is the force measuring surface of the load cell, can make it difficult to balance any calibration tool on the protrusion. No calibration method or tools have been developed that effectively address these problems.
For these reasons, a calibration method for this kind of load cell is highly desirable for the disk fabrication industry. In addition, it is desirable that any such calibration method be practicable with high accuracy and good repeatability.